Calum, Craig, Luis, Georgia, Peter, Travis, Betsy, Filiberto, Ed, Richard, Rich

We had a hard time tracking down the source of an open circuit in a single wire(Y-axis, negative leg of the differential signal sent from the electrometer out from the vacuum system) of the electrometer cabling.  We spent much time taking every section of the cabling apart (air and vacuum) only to find that we couldn't see any problem.  We are absolutely certain that this pin was not functional at the start of our hunt, but somewhere in the process it fixed itself.  Very disturbing.

We were able to verify the performance of all aspects of the design, but as we hoped, we now have a list of tweaks that we will apply to the electrometer back at CIT. A timeseries of the differential signals coming out of the EFM revealed the background noise in the chamber to be of order 50mV pk-pk.  We were able to easily see people moving around in the chamber, and were able to see the door cover being flapped around by Georgia (when we asked her to flap it).

1.  We feel the gain in the EFM should be increased by up to a factor of 100.  We will add a bit of gain inside the EFM, then add more gain to the in-air part of the system.  This is to ensure the background field noise is above the ADC input noise (whitening).
2.  We will improve the mechanical mounting of the calibration plates such that it is easier to shift them from one axis to another
3.  We will improve the robustness of the serial communications link used to adjust the common-mode rejection ratio (CMRR) as this proved problematic.
4.  We want to limit the high frequency bandwidth of the EFM.
5.  We want to investigate a 1.7MHz oscillation seen when the field meter was swung causing an electrical saturation.  It appears to be phase reversal on one of the amplifiers.  This went away upon power cycling.  

We verified that the CMRR can be adjusted in situ to better than -60dB.  We also concluded that this adjustment should be done in-chamber as the bench results taken in the optics lab were different than the results obtained in the installed environment.

We verified the 'dark' noise of the EFM to be approximately 200nV/rtHz at 100Hz, which is consistent with design

We measured the background differential noise in X and Y to be approximately 5uV/rtHz at 100Hz as measured at the differential output at the rack (plots to follow).  I believe the calibration of this device to be approximately 64mV per volts per meter at 100s of Hz or so, although this needs to be further investigated (I get this from 16mv/v/m times 2 for differential sensitivity, times 2 for the differential driver gain).  As Rai cautioned us, we need to be careful with the plate spacing distance due to irregular features between the plates (copper buttons), but a simplifying view is given by the capacitances between the calibration plate - sense plate - and ground of the EFM body.  The observed ambient spectrum seemed a bit devoid of features to me and was approximately a factor of 10 lower than the field observed in the optics lab.